Microorganisms

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Microorganisms show-up every once in a while. It is essential to know 'em.

Microorganisms

Name (disease) Kingdom Size Shape Stains Other (microscopic) Clinical References Image
Aspergillus (aspergillosis) Fungi ? Hyphae that branching
with 45 degrees angle 		PAS-D Fruiting heads when aerobic ? Immunosuppression [1] Aspergillus (WC), Aspergillus cytology (WC)
Zygomycota (zygomycosis);
more specific
Mucorales (mucormycosis) 		Fungi ? Branching hyphae with variable width ? Granulomata assoc. Diabetes, immunodeficient [2] Mucormycosis (homestead.com), Zygomycosis (WC)
Coccidioides, usually C. immitis
(coccidioidomycosis) 		Fungi Large - 20-60 micrometers,
endospores 1-5 micrometers 		Spherules Stains? Other? Immunodeficient [3] Coccidioidomycosis (med.sc.edu) C. immitis (WC)
Histoplasma (histoplasmosis) Fungi 2-5 micrometers Spherical GMS Intracellular (unlike candida), granulomata Source: soil with bird droppings [4] Histoplasmosis (WC)
Blastomyces (Blastomycosis) Fungi 5-15 micrometres Spherical (yeast) Stains? Granulomas, broad-based budding yeast Habitat: Northeast America, Africa [5][6] Blastomyces
Paracoccidioides (Paracoccidioidomycosis) Fungi 6-60 micrometres Spherical (yeast) Stains? Multiple budding "steering wheel" appearance Clinical??? [7] P. brasiliensis (WC).
Pneumocystis jirovecii (Pneumocystis carinii pneumonia; abbrev. PCP) Fungi (previously thought to be a protozoan) 7-8 micrometres "Dented ping-pong ball" GMS Usually in clusters of alveolar casts with a honeycomb appearance HIV/AIDS associated [8] PCP (WC)
Cryptococcosis Fungi 5-15 micrometres Yeast GMS Prominent (i.e. thick polysaccharide) capsule HIV/AIDS associated, most common CNS fungus [9] Crytococcosis - methenamine silver (WC), Crytococcosis - mucicarmine (WC).

Notes:

  • Bold text = key features.

Fungi

  • There are lots of 'em. Below are a few of 'em.

Terminology:[10]

  • Hyphae = microscopic filamentous growth (of fungi) -- single cell.
  • Mycelial = filamentous network of hyphae.
  • Septae/septation = hyphae may be subdivided by septae -- if they aren't they are one mass of protoplasm. (?)
  • Dimorphism = exist in two forms; e.g. single cell (yeast) and mycelial growth.
  • Pseudohyphae = looks like hyphae --but branching pattern is created by separate cells.[11]

Tissue invasive fungi

Typically:[12]

  • Mucor
  • Aspergillus

Histoplasmosis

  • Histoplasma capulatum - primative fungus, typical location: lung.

Coccidiomycosis

Pneumocystis pneumonia (PCP)

  • Pneumocystis jirovecii (used to be called Pneumocystis carinii) - fungus (that used to be considered a parasite), typical location: lung.
    • Clinical: Opportunistic infection. May have subtle finding on chest x-ray.
    • "Dented ping-pong ball" appearance;[16] - remember PCP = ping-pong.
    • Approximately 7-8 micrometres in size - PCP (WP). Several images are here (WC).

Cryptococcus

  • Usually C. neoformans, fungus - opportunistic infection, typical location: lung.
  • Most common fungus seen in CSF specimens.[17]

Appearance:

  • Yeast:
    • Round/ovoid 5-15 micrometres (may resemble Histoplasma or Candida -- but often larger).
    • Thick mucopolysacchardie capsule + refractile centre.[18]
    • "Tear drop-shapped" budding pattern (useful to differentiate from Blastomyces, Histoplasma).[19]

Images:

Cryptosporidiosis

Notes:

  • Cryptosporidium parvum?[20]

Candidiasis

  • Commonly Candida albicans - yeast (fungus), locations: oral cavity, vagina.
  • Dimorphic - seen in two forms:
    • Pseudohyphae[21] - collections of many C. albicans cells in a branching pattern.
    • Yeast form - single cells, 10 to 12 micrometres in diameter, gram positive.[22]
  • Stains: PAS, methenamine silver.
  • Images:

Blastomycosis


Mucormycosis

General

  • Causative organism: Mucorales.
    • Kingdom: Fungi.
    • AKA Zygomycota (zygomycosis).
  • Assoc. with diabetes, immunodeficiency.

Histology

Features:[25]

  • Branching hyphae variable width.
  • Granulomata associated.

Image:


Worms

Strongyloides

  • Lung?

Features:

  • Long worms.
  • ~10-15 micrometers wide.

Echinococcus

  • Echinococcus granulosus.
  • Causes hydatid disease in the liver.

Features:

  • Hooklets.
  • Scoleces - knoblike anterior end of a tapeworm.[26]

Enterobius vermicularis

  • AKA pinworm.

Features:[27]

  • Ovoid eggs - double walled shells, one side flat.


Viruses

Many virus afflicit humans. Only a few of them can be diagnosed histologically.

Viral inclusions

Cowdry types:[28]

  • Cowdry type A inclusion:[29]
    • Round eosinophilic material surrounded by a clear halo.
  • Cowdry type B inclusion:[30]
    • Neuropathology thingy. (???)

Images:

Herpes simplex virus (HSV)

  • Canker sores - usually HSV-1.
  • Genital herpes - usually HSV-2.

Histology/cytology

Features:[31]

  • Clear "ground glass" nuclei.
    • Rim of peripheral chromatin.
  • Nuclear inclusions.
  • Multinucleation with nuclear molding, i.e. multiple nuclei that touch over a large surface area.

Image:

Cytomegalovirus (CMV)

Features:

  • Very large nucleus (as the name implies) with clearing.
  • Granular cytoplasmic inclusions (red on H&E sections).

Images:

See also

References

  1. ↑ APBR P.682.
  2. ↑ APBR P.682.
  3. ↑ APBR P.682.
  4. ↑ APBR P.682.
  5. ↑ APBR P.682.
  6. ↑ http://pathmicro.med.sc.edu/mycology/mycology-6.htm
  7. ↑ APBR P.682.
  8. ↑ APBR P.684.
  9. ↑ APBR P.682.
  10. ↑ http://www.fungionline.org.uk/1intro/3growth_forms.html
  11. ↑ http://pathmicro.med.sc.edu/mycology/mycology-3.htm
  12. ↑ CM 17 Apr 2009.
  13. ↑ WMSP P.103.
  14. ↑ WMSP P.3.
  15. ↑ WMSP P.103.
  16. ↑ WMSP P.103.
  17. ↑ APBR P.682.
  18. ↑ APBR P.682.
  19. ↑ APBR P.682.
  20. ↑ http://www.dpd.cdc.gov/dpdx/HTML/Cryptosporidiosis.htm
  21. ↑ WMSP P.3.
  22. ↑ http://pathmicro.med.sc.edu/mycology/mycology-3.htm
  23. ↑ WMSP P.3.
  24. ↑ PMID 12375640
  25. ↑ APBR P.682.
  26. ↑ http://www.thefreedictionary.com/scoleces. Accessed on: 10 January 2010.
  27. ↑ APBR P.685.
  28. ↑ URL: http://www.pathconsultddx.com/pathCon/largeImage?pii=S1559-8675%2806%2970864-6&figureId=fig3&ecomponentId=mmc3. Accessed: 12 January 2010.
  29. ↑ URL: http://www.whonamedit.com/synd.cfm/3495.html. Accessed on: 22 January 2010.
  30. ↑ http://www.whonamedit.com/synd.cfm/3496.html. Accessed on: 22 January 2010.
  31. ↑ SM. 11 January 2010.
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